1. Technical Field
The present invention relates to a driving technology of a discharge lamp lighted by discharge between the electrodes.
2. Related Art
As a light source used in image display apparatuses such as projectors, there is used a high-intensity discharge lamp such as a super high-pressure discharge lamp. In such a super high-pressure discharge lamp, the arc used as the light source is formed between projections provided to the electrodes. Therefore, it is proposed that the projections are formed on the tips of the electrodes, and in order for forming the arc originated from the projections, an alternating current having a signal with a frequency lower than a stationary frequency inserted in a signal with the stationary frequency is supplied to the super high-pressure discharge lamp (see, e.g., JP-A-2006-59790).
Further, it is proposed that in order for stabilizing the arc bright spot in the case in which the current (a lamp current) supplied to the super high-pressure discharge lamp is reduced due to rise in the voltage (the lamp voltage) between the electrodes of the super high-pressure discharge lamp or reduction in the lighting power, an alternating current having a signal with a lower frequency inserted is supplied to the super high-pressure discharge lamp under the condition of reducing the lamp current (see e.g., JP-A-2006-332015).
However, even if the alternating current having a signal with a lower frequency inserted is supplied to the super high-pressure discharge lamp under the condition of reducing the lamp current, the projections with preferable shapes may not be formed depending on the conditions of the electrodes, and flickers caused by migration of the bright spot of the arc might occur. This problem not only arises under the condition of reducing the lamp current, but also arises commonly in driving the discharge lamp under the condition apt to cause flickers such as an exhausted electrode.